Refrigeration system with compressor unloading means



Jan. 14, 1964 Fil Fig.1

[l8 fl G. w. HARTWELL 3,117,425

REFRIGERATION SYSTEM WITH COMPRESSOR UNLOADING MEANS ed Oct. 24, 1960 3 Sheets-Sheet 1 Fig.2

INVENTOR.

George W. Hartwell BY Giff/5L 1419/ /29} A TTORNEYS Fig.3

Jan. 14, 1964 w. HARTWELL 3,117,425

REFRIGERATION SYSTEM WITH COMPRESSOR UNLOADING MEANS Filed Oct. 24, 1960 5 Sheets-Sheet 2 I40 INVENTOR. George W. Hartwell Gut/g Marni, d WM A T TOR N E YS Jan. 14, 1964 Filed Oct. 24, 1960 Fig.8

a. w. HARTWELL REFRIGERATION SYSTEM WITH COMPRESSOR UNLOADING MEANS 3 Sheets-Sheet 5 INVENTOR. George W. Hartwell A TTORNEYS United States Patent 3,117,425 REFRIGERATEQN SYSTEM WITH COMPMSSOR UNLOABING MEANS George W. Hartwell, South Hadley, Mass, assignor to Dunham-Bnsh, Inc., Hartford, Conn. Filed Oct. 24, 1960, Ser. No. 64,602 17 Claims. (til. 62-196) This invention relates to refrigeration, and more in particular to refrigeration systems of the compressor type, wherein the compressor is unloaded automatically. This invention also relates to compressor and auxiliary components and systems.

An object of this invention is to provide improved refrigeration systems. A further object is to provide improved refri erant compressors having means to automatically reduce the capacity. A still further object is to provide a mechanism which automatically controls the amount of gas which is pumped by the compressor in a system having a plurality of compressor cylinders. Another object is to provide an improved mechanism for unloading compressors during start-up. A still further object is to provide for the above with apparatus which is sturdy and light weight in construction, efiicient and dependable in use, and which is adaptable to meet varying demands and problems in the industry. These and other objects are in part obvious, and in part pointed out below.

In the drawings:

FIGURE 1 is a somewhat schematic representation of one embodiment of the invention;

FIGURE 2 is a sectional view of a portion of one cylinder of the compressor of FIGURE 1 and the unloader control unit for the cylinders;

FIGURES 3 and 4 are fragmentary sectional views similar to a portion of FIGURE 2, but showing different positions of the operating parts;

FIGURE 5 is an enlarged sectional view on the line 55 of FIGURE 4;

FIGURE 6 is a fragmentary sectional view on the line 66 of FIGURE 5;

FIGURE 7 is a somewhat schematic view illustrating the sequential unloader control for the various cornpressor cylinders;

FIGURE 8 is an exploded view of the unloader control unit; and,

FIGURE 9 is a fragmentary perspective view of the cylinder unloader mechanism.

In a refrigeration system having a compressor, it is desirable to substantially unload the compressor during the start-up period while the compressor is being brought up to speed. Also, it is desirable to reduce the compressor capacity of a refrigeration system when the load on the system drops oif. That is, when the refrigerant load on a refrigeration system drops substantially below the full operating capacity, it is desirable to reduce the effective rate at which refrigerant is being compressed by the compressor or the compressors. The present in vention solves the problem of unloading the compressor during start-up, and provides the desirable flexibility of compressor capacity for the refrigeration system. The present invention also provides an improved refrigeration system in which the capacity of the system is varied automatically when there are variations in the load. The present invention insures eificient operation at all times, and overcomes difficulties and malfunctioning which can result :from operating the system with excess compressor capacity. The present invention also provides improved operation of refrigeration systems, particularly in that there is stability in the over-all operation.

Referring to FIGURE 1 of the drawings, a refrigeration system has a compressor 2 driven by a motor 12, a

condenser 4, a receiver 6, an expansion valve 8 and an evaporator 10. The compressor has five cylinders 16, 17, IS, 19 and 20, which discharge into a header 21 from which the compressed refrigerant passes to condenser 4. The present invention is concerned with compressor unloading and a control unit 14 which controls the unloading.

In the illustrative embodiment of the invention, a gradual decrease in the refrigeration load operates to reduce the operating capacity of compressor 2. The reduction is by steps, and is effected by causing four of the five cylinders to be unloaded one at a time as the load decreases. That is, the four cylinders are unloaded in sequence, each causing a drop of twenty percent in the compressor capacity, so that the compressor capacity may be 190%, 60%, 40%, or 20%. The control unit 14 is also effective to unload all four of these cylinders when the compressor stops. This permits motor 12 to start the compressor without difliculty. When the compressor has reached substantially full speed, the control unit 14 loads the other four cylinders, so that the compressor operates at full capacity. Thereafter, the cylinders are unloaded individually as the load drops off. However, the control unit maintains stability of operation, even though the unloading or loading of a cylinder may tend to produce an over correction which might cause hunting with prior systems of control.

As illustrated in FIGURE 1, the suction line from evaporator 10 extends to the compressor crankcase, and the interior of the crankcase is therefore on the suction or low side of the system. The schematic representation indicates that the compressed gas is discharged from the individual cylinders to a header, although this header is formed by interconnecting passageways within the compressor. Referring now to FIGURE 2, one cylinder 2d of the compressor 2 is shown, together with the control unit 14 and the adjacent portion of the compressor crankcase 22. Cylinder 20 has a cylinder liner 24, a piston 26, a piston rod 28, an inlet valve plate 30, a head plate 31 carrying an exhaust or outlet valve assembly 32, a cylinder head 34 and a valve plate retaining spring 36. During operation, the low-pressure refrigerant gas passes (FIGURE 1) from the evaporator 10 to the compressor crankcase 22 from which it is withdrawn into the various cylinders and compressed. The compressed refrigerant from each cylinder is discharged into the cylinder head and flows into the header 21 formed by interconnecting passageways, including passageway 38 in FIGURE 2. The low pressure refrigerant is drawn from the crankcase through passageways 40 and an annular valve passageway or opening 42 in the cylinder liner. Seated over the valve opening 42 is 'an annular valve ring 44- which is urged toward its valve closing or seated position by a plurality of evenly-spaced, compression coil springs 46, each of which rests at its top in a recess in the valve plate. During operation, piston 26 moves up and down in cylinder 24 and, during each downward movement or intake stroke, low pressure refrigerant gas is drawn into the cylinder from the crankcase through passageway 40 and valve opening 42. Valve ring 44 is lifted by the difference in pressures so as to permit the free entry of the gas to the cylinder. When the piston then star-ts its up stroke, the valve ring 44 seats again under the action of springs 46, and the refrigerant gas is compressed and discharged through the outlet valve assembly 32.

Valve ring 44 is accurately positioned and guided in its movement by engagement at its outer periphery (see also FIGURE 9) with the inner wall of an annular unloader piston 48 which is slidably mounted in an annular unloader cylinder 60 in the valve plate 30. At the bottom of unloader piston 48, there is an inner peripheral flange 52 which is positioned beneath the outer periphery of valve ring 44 so that the valve ring is lifted when the unloader piston moves upwardly. The valve piston is .urged upwardly by a plurality of spaced coil springs 54, each of which is nested in a cylindrical recess in the bottom surface of the unloader piston. The unloader piston is moved up and down by controlling the pressure above itin a manner explained below.

. The control unit 14 (FIGURE 2) operates automatically to selectively connect high or low fluid pressures to the various unloader cylinders 50 of the four compressor cylinders. In this embodiment, the high fluid pressure is from the high side, i.e., the compressed refrigerant gas from the cylinder head 34; and, the low fluid pressure is from the low side, i.e., the refrigerant gas from crankcase 22. When the high pressure gas is connected to unloader cylinder i) of the compressorcylinder 29, the unloader piston 48 is moved downwardly against the action .of springs 54 to. the position shown in FEGURE 2. The piston flange 52 therefore permits the valve ring 44 to seat under the action of springs 46. Cylinder 24 is then loaded and operates to compress refrigerant, as outlined above. When it is desirable to unload cylinder 20, the low pressure gas is connected to unloader cylinder 59, and this causes the unloader piston to move upwardly so that its flange 52 lifts the valve ring 44 so that it cannot seat during the up-stroke of the piston, and this unloads the cylinderlll. During each up stroke, the inlet valve is held open so that refrigerant moves out of the valve, and the refrigerant is not compressed, as described above.

The construction of control unit 14 can be understood best by referring to FIGURE 8 which shows the various parts in perspective, with some being shown in section. This control unit has a cylindrical unloader control body 60 which has press-fitted therein a control cylinder 62. Beneath the control body and clamped thereto by a pair of screws 61, is a valve block 64 having a valve cavity .65 within which a valve piston 65 is mounted. Respectively above and below the valve block 64 are gaskets .68 and 70. Slidably mounted in an axial bore 72 in the control cylinder 62 is a valve spindle 7 i of a control valve member 74, which has an enlarged top portion s.

Directly above valve member '74 is a bellows 76 having an upwardly dished bottom wall 75 against which the top of valve member 74 rests. Above bellows '76, there is a compression coil spring 73, a spring control sleeve 89, and a control screw 82 threaded in sleeve 8t). Spring 78 presses downwardly against the bottom wall of the bellows, and is adjustably held at its upper end by sleeve 3%; and screw 82. This assembly is held by a spring retainer 84 which has an enlarged threaded portion 86 screwed into the upper threaded portion of the valve body 6d, and clamping flanged top of bellows 76 place. Spring retainer 84 has an integral cylinder 85 projecting inside the bellows and providing a stop which limits the upward movement of the bottom wall of the bellows. A cap 83 is threaded into the top of the valvebody.

As indicated above, the central portion of bellows 76 is. urged downwardly by adjusting spring 73, and the upper end of spring 7-8 rests against spring control sleeve fill-the position of which is controlled by the adjusting control screwBZ. The square upper end 83 of screw 82 extends through an opening in the top of the spring retainer 84, and may be engaged by a wrench to turn the screw. The screw has a spring clip d5 which is held in a slot in the screw and cooperates with the shoulder on the screw to provide a journal mounting for the screw in the spring retainer. Sleeve 8% carries a pair of oppositely disposed radial pins 87 which pro ect through a pair of slots 39 in the cylindrical side wall of the spring retainer. In this way, sleeve 89 is held from rotation, and the turning of screw 82 moves sleeve 8 up and down within the spring retainer so as to adjust the pressure which spring 73 exerts upon the bottom wall of the bellows. An opening 91 in the side of the valve body insures that the air within the valve body is at atmospheric pressure. Thus, the top of the bellows wall is urgeddownwardly by atmospheric pressure and the force of spring '78.

Bellows '76 is positioned in a chamber 26 in control body 60, and this chamber is connected through a bore 12d in the control body and a bore 127 in valve block 64 to the interior of the crankcase which is on the suction or low side of the compressor. Hence, the low side or suction pressure is effective upon the bottom of the bellows wall '75. Control valve member 7d is urged upwardly by the pressure in the lower end of the bore 72, so that it is held against the bellows Wall 75;, and this additional force is exerted upwardly on the bellows wall. This high pressure gas is supplied to the various unloader cylinders to move the unloader pistons downwardly, and thereby render them ineffective, thus to load the cylinders. The supplying of this high pressure gas to the various unloader cylinders is controlled by moving the control valve member up and down within bore 72. The

high pressure gas in the lower end of bore 72 urges control valve member '74 upwardly. Referring again to FIG- URE 2, the bottom portion of the control body 6% and the valve block 64 are snugly received in a recess 94 in the wall of the crankcase, and are held in place by a pair of stud bolts 2.

The valve cavity 65 in valve block 64 is formed by an upper large-diameter cylinder 96, and a lower smalldiameter cylinder 98. The bottom of cylinder 98 is connected through a chamfered bore or opening 109 to a metal tube 162 which extends through the crankcase and is connected at its other end to the high pressure compressed refrigerant in the cylinder head 34. The valve piston 66 has upper and lower piston portions 104 and 106 which are provided with 0 rings and are positioned in the respective upper and lower cylinders 96 and 93. Beneath the small diameter piston portion lil, valve body 66 has a hemispherical valve portion 1% which is adapted to seat against the chamfered upper end of bore it'll), thus to form a valve 169 adapted to close off the bottom of the chamber formed by cylinder 83. At the top, the valve piston 66 has a similar but larger hemispherical valve portion llll which is adapted to seat against the chamfered lower end of bore 72, thus to form a valve 111 which is adapted to close between the chamber at the top of cylinder 96 and the bottom ,jof bore '72. Valve piston 66 has an axial bore 112 which extends downwardly from its top to the top of the valve portion res where it intercepts a pair of bores I14 extending radially outwardly to the chamber formed by cylinder 98. Hence, bores 112 and 11 i provide a passageway through valve piston 66 between cylinder 98 and bore 72. When valve W9 is opened by the lifting of the valve portion 1%, bore '72 is connected to hole llll), and the closing of this valve breaks this connection. Valve piston 65 is urged downwardly by a compression coil spring 116, positioned in an annular groove 118 in control cylinder 62 and pressing against the top of the valve piston.v In this embodiment, valve piston 66 is made of Teflon which is polytetralluoroethylene. Under some circumstances, this valve piston may be made of metal.

7 As represented schematically in FIGURE 2, mounted on the outer wall of thecornpressor crankcase 22 is an oil pump 3.13 which isconnected to the compressor drive shaft and operates whenever the compressor motor is operated. Pump 113 withdraws oil from the bottom of the crankcase, and circulates it to the compressor bearing surfaces. Pump 113 is alsoutilized to control the loading and unloading of four of the live cylinders of the compressor during startup. Accordingly, connected to the outlet of the purnp is an oil pipe or line 115 which extends through the crankcase to the bottom of cylinder 96 beneath piston 2& Therefore, when the compressor is operating, the oil pump maintains suflicient oil pressure beneath piston 1% to hold valve piston 6% in the elevated position of FIGURE 2. In this way, valve 109 an /A25 in the high pressure line is maintained open, ahd valve 111 at the lower end of bore 72 is maintained closed. This insures the maintaining of the high pressure refrigerant supply to the bottom of bore 72 as long as compressor cylinder 19 is operating, and the oil pump is operating properly. The top of cylinder 96 is connected (see FIGURE 8) to the low side by a slot 117 at the top of valve block 60 between the cylinder and bore 127 which is open (see FIGURE 2) to the low side pressure in the crankcase. This provides a vent above piston 104 which insures against sluggish upward movement of the valve piston. As will be explained below, this low pressure is also utilized to obtain unloading during startup.

As indicated above, slidably mounted in bore 72 of control cylinder 62 is the valve spindle 71 of the control valve member 74. The valve spindle 71 has five lands which snugly fit bore 72 and form gas-tight seals, and which are defined by reduced diameter portions of the valve spindle. The central land 73 has above it a lowpressure annular passageway 75, and beneath it a high pressure annular passageway 77. During operation, passageways 75 and 77 provide passageways through which the high and low gas pressures are made available to effect the unloading and loading of the cylinders. Control valve member 74 has at the top a cross bore 121 which intercepts an axial bore 123 which extends downwardly to a radial bore 125 (see FIGURE 6) which connects with the annular low-pressure passageway 75. Extending upwardly from the lower end of control valve member 74 is axial bore 122 which is connected through a radial bore 124 to the high pressure annular passage way 77 Referring also to FIGURE 5, the control cylinder 62 has four bores 126, 127, 128 and 129, each of which is formed by an extremely small bore 130 extending radially outwardly from bore 72, and an enlarged bore 132 connected thereto. Bores 126 to 129 are connected to slots 134 to 137, respectively, in the valve body. Referring again to FIGURE 2, slot 134 is connected to bores 138 and 140 in the valve body, bore 142 in the valve block 64, a metal tube 144, a bore 146 in the cylinder liner, and passageway 148 to the unloader cylinder 50 of the compressor cylinder 20. Referring now to FIGURE 8, valve block 64- has bores 150, 152 and 154 which are identical with bore 142, and each of which is connected with bores in valve body 60 similar to bores 140 and 138, so as to provide connections with slots 135 to 137, respectively. Metal tubes similar to tube 144 connect bores 150, 152 and 154, respectively, to the unloader cylinders of the compressor cylinders 16, 17 and 18. Therefore, each of the bores 126 to 129 is connected to provide a fluid pressure control connection with the unloader cylinder of its compressor cylinder.

Referring now to FIGURES 2 and 6 which show cylinder 20 and its associated mechanism, control piston 74 is positioned to connect the high pressure refrigerant from the compressor header 34 through pipe 102, bore 100, valve cylinder 98, bores 114 and 112, the chamber formed at the lower end of bore 72, bores 122 and 124, bore 126, slot 134, bores 11%, 140, and 142, pipe 144, bore 145 and passageway 143 to the unloader cylinder 50. This positions unloader piston 48 downwardly against the action of springs 54 to the position shown, so that valve 44 is free to seat on its valve opening. Therefore, compressor cylinder operates to compress the refrigerant gas, as outlined above.

FIGURES 3 and 4 show the pertinent portions of cylinder 20 and control unit 14, respectively, during startup and during operation of the compressor with cylinder 20 unloaded. Referring to FIGURE 4, when the control valve member 74 moves downwardly, the low pressure is connected through bores 121, 123 and 125, and the annular passageway 175 to bore 126, and thence to the unloader cylinder. This reduces the pressure in the unloader cylinder so that springs 54 raise the unloader 5 piston, and this lifts the valve from its seat so as to unload the cylinder.

It has been pointed out above that the illustrative embodiment of the invention utilizes the high and low pressures of the refrigerant in the refrigeration system to provide the operating medium for performing the unloading operations. It should be noted that springs 54 actually raise the unloader piston 48 and the valve member or plate. The high pressure refrigerant forces the piston downwardly against the action of these springs, so that the power thus stored is available when the suction pressure is connected to the unloader cylinder, thus to Withdraw the high pressure refrigerant. Springs 54 act in a uniform manner, and the lifting force is exerted by piston flange 52 around the entire periphery of the valve ring 44. The invention contemplates that other specific means may be provided for effecting the actual unloading and loading operations, utilizing power supplied by the high and low-pressure refrigerant.

In the illustrative embodiment of the invention, each of the bores 126 to 129 (see FIGURES .5 and 6) terminates at the control bore 72 in a port having a diameter of .022 inch, and the land or sealing ring 137 on the valve spindle 71 has a width of .030 inch. Hence, each port is completely covered during each upward and downward movement of the valve spindle during movement of the order of .008 inch. For example, as the valve spindle moves downwardly it first covers and seals the port for bore 126. t must then move an additional .008 inch downwardly before it opens this port to the suction pressure and, during this movement, cylinder 20 remains loaded. Assuming that the further movement of the valve spindle unloads and opens bore 126 to the suction pressure, cylinder 20 is immediately unloaded. If the suction pressure now increases slightly, the valve spindle moves upwardly and covers the port of bore 126 again. However, cylinder 20 remains unloaded until the valve spindle moves upwardly an additional .008 inch before the bore is again open to high pressure and cylinder 20 is loaded. If the load on the system is satisfied by the reduced compressor capacity with cylinder 20 unloaded, the valve spindle will not move the additional .008 inch, and therefore cylinder 20 remains unloaded. Therefore, the added movement of the piston allows the suction pressure to adjust to the reduced capacity of the compressor before cylinder 20 is reloaded, and this insures stability of operation. The operation is the same during the unloading of the other cylinders, and a corresponding operation occurs during the loading of each of the cylinders. In this way, the compressor capacity and the suction pressure are maintained stable during wide variations in the load.

The ports for the respective bores 126 to 129 are spaced axially along the control bore .008 inch from each other, center to center. Therefore, the land or sealing ring 137, which is .030 inch wide, is partially covering one port, while it is completely covering the next adjacent port. The four cylinders are unloaded in accordance With a predetermined sequence, and are loaded again in the reverse sequence. In each sequence, there are three intermediate steps and, in this embodiment, the control is such that a change in suction pressure of the order of 2%. pounds causes the unloading or loading of a cylinder. Initially, control unit 14 is adjusted to the unloading control point by turning screws 82, which adjusts the pressure exerted by spring 78, until the unloading of cylinder takes place at the desired suction pressure. Thereafter, the other cylinders 16, 17 and 18 are unloaded individually and in accordance with the predetermined sequence upon successive drops or unloading steps of 2 /2 pounds in the suction pressure. There being three intermediate unloading steps of 2 /2 pounds each, there is a total drop of 7 /2 pounds between the unloading of cylinder 20 and the unloading of the last of the other three cylinders. This drop in suction '2 pressure amounts to a correspond ng temperature change of the order of F. for R22 refrigerant systems, and of the order of 8 F. for R12 refrigerant systems. The control range during gradual loading of the four cylinders is identical, and the general operating mode is identical, but in reverse.

As pointed out above, bellows "76 (see FIGURE 2) is positioned within the chamber 126, so that it causes the suction or low-side pressure of the refrigerant to act against atmospheric pressure to produce a net force upwardly in FIGURE 2. Also, when the compressor is operating, the high-side or high pressure refrigerant exerts an upward force upon the lower end of spindle 71, and this force is transmitted to the center of the bellows diaphragm or bottom wall. Therefore, the total upward force acting upon the bellows diaphragm is the sum of" the area of valve spindle 71 times the difference between high side refrigerant pressure and the atmospheric pressure; and, the area of the diaphragm minus the area of the valve spindle times the diiference between the flow side refrigerant pressure and the atmospheric pressure. Spring '78 has such characteristics and is so adjusted as to balance this sum of upward forces throughout the operating range. When the upward forces are above this range, the cylindrical portion or stop member 85 limits upward movement of the bellows diaphragm. When the upward forces are below this range, the downward movement of the diaphragm is limited by the engagement of the shoulder on valve member 74 at its enlarged upper end. Variations in the high-side pressure of the refrigerant cause some variation in the upward pressure exerted on the valve spindle, but these variations are inconsequential with respect to the unloading control. That is, these variations are insignificant within the range of operation wherein loading and unloading of the cylinders take place, and variations at other times may be disregarded.

It has been pointed out above that the refrigerant and lubricating oil constitute operating components of the refrigeration system, and also of the unloader control system. It has also been pointed out that the power for operating the unloader mechanisms comes from the refrigerant, even though the actual lifting of the valve plates is performed by compression springs. The utilization of the refrigerant and the oil for these control and operating functions is particularly advantageous because this makes it possible to eliminate factors of construction and operation which might cause malfunctioning, and which are otherwise objectionable. The refrigerant gas will not cause corrosion or stoppage in the control and unloading mechanisms, and it is completely free of dirt or other foreign materials. Also, even if there were leakage of refrigerant or oil from one chamber or passageway to another, the operation of the refrigeration system would not be seriously impaired. Hence, the refrigeration system which constitutes the illustrative embodiment is a self-contained system which requires no external materials or elements to operate in an eflicient manner through a wide range of operating capacity.

It will be appreciated that certain phases of the invention may be practiced by the use of fluids other than the refrigerant as the unloading control and operating medium. Also, certain components of the system may be utilized in systems different from the illustrative embodiment, without departing from the scope of the invention.

As many possible embodiments may be made of the mechanical features of the above invention and as the art herein set forth might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limitin. sense,

I claim:

1. In a relrigeration system, the combination of, a condenser, restrictor means, evaporator means, a compressor having a plurality of cylinders and adapted to withdraw refrigerant from said evaporator means and deliver it at increased pressure to said condenser, one of said cylinders of said compressor having a suction valve which is adapted to be held away from its valve-closing position thereby to unload the cylinder, unloader unit means for moving said suction valve to its cylinder unloading position in response to the connection of said unloader unit means to the suction pressure of the compressor and for moving to a cylinder loading position in response to connection with the high pressure compressed refrigerant, and an unloader control unit having a valve mechanism which is adapted to connect said unloader unit means alternatively to the high pressure refrigerant or the suction pressure refrigerant in response to increases and decreases in the suction pressure, said unloader unit means including an unloader cyiinder and piston assembly which is adapted to move to and from acylinder unloading position upon being connected to the suction pressure and the high pressure of the refrigerant, respectively, said suction valve being an annular plate at the periphery of its cylinder and said unloader unit means including an annular unloader piston surrounding said annular plate and providing a peripberal guide wall there- 1 for and having a flange portion which extends radially inwardly beyond the outer periphery of said annular plate and which is moved by the movement of said annular piston to hold said annular plate away from its valve seat.

2. A refrigeration system as described in claim 1 which includes an oil pump to supply oil under pressure to said compressor, and means responsive to the operation of said oil pump to insure the unloading of said suction valve when said oil pump is not operating and to render said unloader control unit operative to control the loading and unloading operation when said pump is operating.

3. A refrigeration system as described in claim 1,

wherein said compressor includes, one cylinder which is always loaded, and a plurality of cylinders, each of which includes a suction valve and an unloader unit means for moving its suction valve to its cylinder unloading position wherein said unloader unit means includes means to render said unloader units ineffective sequentially and thereby load said plurality of cylinders in sequence under the control of said unloader control unit. 7 4. A refrigeration system as described in claim 1, wherein said compressor includes a plurality of said unloader unit means each of which is associated with a compressor cylinder and all of which are controlled by said unloader control unit.

5. A refrigeration system as described in claim' 1, wherein said valve mechanism of said unioader control unit comprises, a control valve, and pressure responsive means which moves said control valve in response to changes in the suction pressure.

6. A refrigeration system as described in claim 5, wherein said pressure responsive means comprises a bellows and mounting means therefor and providing a body of refrigerant gas at one side of the bellows.

7. A refrigeration system as described in claim 6 which includes means to prevent the supplying of compressed refrigerant to the compressor of said unloader unit means during the start-up period of said compressor.

8. In anunloader control for a compressorina refrigeration system, the combination of, a shell construction, a control valve which has a plurality of spaced and relatively fixed parts and a control member slidably mounted with respect to said shell construction and having a pair of refrigerant gas passageways which are alternatively exposed to said plurality of spaced and relatively fixed ports, means to supply refrigerant at the suction pressure of the compressor to one of said gas passageways, means to supply compressed refrigerant to the other of said gas passageways, a valve control unit which is connected to slide said control member with respect to said ports in response to changes in said suction pressure, and an auxiliary valve means which is adapted to move to a rest position when the compressor is stopped and which includes a valve which cuts oil the supply of compressed refrigerant to said gas passageway.

9. An unloader control as described in claim 8, wherein said auxiliary valve comprises a valve body having a pair of concentric and adjacent cylinders of different diameters, a valve piston having a pair of piston portions seating and slidably mounted in said cylinders and having axially positioned valve portions protruding from th opposite ends thereof, means forming concentric gas inlet and outlet ports presenting valve seats which are adapted to mate with the respective valve members upon movement of said valve piston axially in said cylinders, said valve piston having a passageway bypassing one of said cylinders and opening into the other.

10. An unloader control as described in claim 8 which includes a spring urging said valve piston axially, and means to supply oil under pressures to move said valve piston against the action of said spring.

11. In a refrigeration system, the combination of, a condenser, restrictor means, evaporator means, a com pressor having a plurality of cylinders and adapted to Withdraw refrigerant from said evaporator means and deliver it at increased pressure to said condenser, one of said cylinders of said compressor having a suction valve which is adapted to be held away from its valveclosing position thereby to unload the cylinder, an unloader unit which is adapted to move said suction valve to its cylinder unloading position in response to the connection of said unloader unit to the suction pressure of the compressor and which is adapted to move to a cylin der loading position in response to connection with the high pressure compressed refrigerant, and an unloader control unit having a valve mechanism which is adapted to connect said unloader unit alternatively to the high pressure refrigerant or the suction pressure relrigerant in response to increases and decreases in the suction pressure, said unloader unit including an unloader cylinder and piston assembly which is adapted to move to and from a cylinder unloading position upon being connected to the suction pressure and the high pressure or" the refrigerant, respectively, said piston of said cylinder and piston assembly having an integral flange member which is positioned in overlapping relationship to said suction valve thereby to provide a one-way mechanical connection therewith.

12. In a refrigerant compressor, the combination of, a compressor casing construction providing a plurality of cylinder components with interconnecting passageways between exhaust ports from each of the cylinders and providing inlet passageways from the crankcase into each of the cylinders, each of said cylinders being provided with a piston and intake and outlet valves, the intake valve for one of said cylinders comprising a substantially annular port and an annular valve member at the periphery of the cylinder and adapted to open and close in response to changes in pressure during the intake and compression strokes of the piston, cylinder and piston means at the periphery of said valve member and having interengaging means which is adapted to hold said valve member from closing when the piston means is moved to an active position from an inactive position, spring means to bias cylinder and piston means, means to supply fluid to said cylinder and piston means to move said piston means against the action of said spring means, a control valve, means to move said control valve in response to changes in the suction pressure of the compressor, means connecting the high-pressure refrigerant to one side of said control valve, 163 15 wnnecting the suction pressure to the other side of said control valve, and means connecting said cylinder and piston means to said control valve, said control valve being adapted to be moved from one position wherein it connects the suction pressure to said cylinder and piston means to a position wherein it connects the compressed refrigerant pressure to said cylinder and piston means in response to variations in the suction pressure.

13. A refrigerant compressor as described in claim 12, wherein said compressor has a plurality of cylinders provided with annular valve members and cylinder piston means as described and connected to said control means.

14. A refrigerant compressor as described in claim 13, wherein said control means comprises a valve spindle slidably mounted in a bore and having a plurality of ports opening to said bore and spaced axially and arcuately therein, and which includes means providing separate passageways from said ports to the respective cylinder and piston means.

15. In a refrigeration system wherein the load varies over a wide range, the combination of, a multicylinder compressor the suction pressure of which drops with a reduction in the load, an oil pump to circulate oil for lubri eating said compressor and adapted to produce an elevated oil pressure at its outlet, pressure responsive means which is connected to the outlet of said oil pump and is responsive to the building up of the oil pressure to a predetermined value said comprcssor has been started and has reached its normal operating speed, unloader means which is operative to unload certain predetermined cylinders of said compressor, means operatively connected to said pressure responsive means and operative to render said unloader means ineffective when oil pressure has reached said predetermined value during the starting up of said compressor, and means responsive to a drop in the suction pressure of said compressor to render said unloader means efiective to unload one cylinder of said compressor upon the dropping of the suction pressure of said compressor to a predetermined value.

16. Apparatus as described in claim 15 wherein said last named means is effective to unload a plurality of cylinders of said compressor in sequence and in response to equential reduction of the suction pressure to predetermined values.

17. A refrigeration compressor having an oil circulating means which produces a predetermined oil pressure at its outlet when the compressor has been brought up to speed, unloader means for unloading one cylinder of said compressor, means utilizing the compressed refrigerant of a loaded cylinder to render said unloader ineffective, means utilizing the suction pressure of said compressor to operate said unloader and thereby unload said cylinder, and means responsive to said oil pressure at said outlet to render said unloader ineffective at the end of the starting up period of said compressor.

References Cited in the file of this patent UNITED STATES PATENTS 

17. A REFRIGERATION COMPRESSOR HAVING AN OIL CIRCULATING MEANS WHICH PRODUCES A PREDETERMINED OIL PRESSURE AT ITS OUTLET WHEN THE COMPRESSOR HAS BEEN BROUGHT UP TO SPEED, UNLOADER MEANS UTILIZING THE COMPRESSED REFRIGERANT OF A LOADED CYLINDER TO RENDER SAID UNLOADER INEFFECTIVE, MEANS UTILIZING THE SUCTION PRESSURE OF SAID COMPRESSOR TO OPERATE SAID UNLOADER AND THEREBY UNLOAD SAID CYLINDER, AND MEANS RESPONSIVE TO SAID OIL PRESSURE AT SAID OUTLET TO RENDER SAID UNLOADER INEFFECTIVE AT THE END OF THE STARTING UP PERIOD OF SAID COMPRESSOR. 